Machine tools, carrying machines, coordinate measuring machines, image measuring machines and the like employ a mechanism for controlling a position and a speed of an object to be moved. In such a mechanism, when acceleration of the object rapidly changes, vibration is sometimes caused to the object. Studies have been made for solving the above disadvantages (see, for instance, Patent Literature 1: JPA-2006-202019).
The structure disclosed in Patent Literature 1 includes an acceleration sensor provided to an object.
When the object is to be moved by a motor, a speed command is calculated based on a position command and a position feedback signal. Further, acceleration of the object is detected and a correction value is calculated based on the detected acceleration. Then, after a corrected speed command is calculated by subtracting the correction value from the speed command, a current command is calculated based on the corrected speed command and a speed feedback signal. Subsequently, a command to the motor is calculated based on the current command and a current feedback signal, and the object is moved by the motor based on the calculated command.
In the structure as disclosed in Patent Literature 1, even when the acceleration of the object does not change, the load torque of the motor may vary depending on the speed and the position of the object. However, according to the structure disclosed in Patent Literature 1, the motor cannot be controlled in response to the variation in the load torque, so that a speed control performance for the object becomes unstable.